In general, the orthodontic treatment is a dental procedure for moving maloccluded teeth to ideally occluded positions and performed by using an orthodontic appliance.
The orthodontic method is classified into a labial orthodontic method in which the orthodontic appliance is bonded to a tooth surface facing the outside of an oral cavity to perform the orthodontic treatment and a lingual orthodontic method in which the orthodontic appliance is bonded to a tooth surface facing the tongue to perform the orthodontic treatment. In recent years, the lingual orthodontic method by which the orthodontic appliance is not exposed to the outside is preferred.
A conventional orthodontic appliance used for the orthodontic treatment includes a bracket bonded to teeth of a patient and an arch wire ligated to a slot defined in the bracket to provide pulling force for moving the teeth respectively to orthodontic positions.
The orthodontic treatment using the conventional orthodontic appliance is performed such that the mass-produced bracket having a predetermined shape is bonded to the teeth of the patient, and then the arch wire is bent to correspond to an ideal dental arch (curvature of teeth) and ligated to a bracket slot.
However, since the above-described conventional orthodontic appliance includes the bracket that is mass-produced to have the predetermined shape without considering shapes of the tooth and teeth of the patient, and bonding of the bracket to the teeth of the patient and fitting to form the arch wire to the ideal dental arch shape are dependent on a competence level of an operator, the bonding of the bracket to an exact position of the tooth and the forming of the arch wire at an exact curvature are extremely difficult.
Thus, when the conventional orthodontic appliance is used, successful orthodontic treatment is not guaranteed
To improve the above-described problem of the conventional orthodontic appliance, various kinds of orthodontic appliances and methods thereof have been developed. In recent years, the orthodontic appliance customized to the patient based on rapid prototyping and the method of fabricating the same have been developed.
Briefly referring to technical contents related to the orthodontic appliance fabrication disclosed in Korean Patent Publication No. 10-2012-0101086, an orthodontic setup model showing the predicted post-treatment is fabricated, and then a base to be bonded to each of tooth surfaces is numerically designed to be fabricated by using the rapid prototyping.
Thereafter, a mass-produced bracket body having a linear bracket slot is fixed to an appropriate position of the base, and the arch wire is fabricated by the numerical design to be inserted into the bracket slot and then fabricated to correspond to a curvature of the dental arch after the orthodontic treatment.
Since, in the orthodontic appliance fabricated as described above, the base is relatively accurately fit to the tooth surface after the ideal orthodontic treatment for the patient, and the arch wire has the curvature corresponding to the dental arch after the orthodontic treatment, the orthodontic treatment is satisfactorily performed relative to the conventional orthodontic treatment procedure.
However, the above-described conventional orthodontic appliance has problems as follows.
Since the orthodontic bracket, as a mass-produced stock bracket, has the linearly processed bracket slot into which the arch wire is inserted, the linearized slot may not accurately correspond to the curvature of the arch wire fabricated to fit to the dental arch after the orthodontic treatment for the patient.
Thus, when the arch wire is inserted into the bracket slot, the linearized slot is not shape-matched to the curvature of the arch wire. In detail, in case of a labial orthodontic treatment, the arc wire substantially contacts both end areas in a longitudinal direction of the bracket slot, and in case of a lingual orthodontic treatment, the arc wire substantially contacts one point of the bracket slot.
Due to this, the arch wire having the curvature may not completely close-contact the linearized slot not to expect the exact pulling force and pulling position. In particular, the pulling force for orthodontic-treating a protruding angle of the tooth may not be provided. This may cause a serious problem in ideal orthodontic treatment.
When the base is custom-fabricated by using the setup model showing post-treatment occlusion, the base may be bonded to an exact position of the tooth without much difficulty. However, since the body portion including the bracket slot still uses a mass-produced stock product and is assembled to the base, a final bracket profile is raised and the bonding of the base at the exact position is difficult.
As described above, when the bracket profile is raised, irritation sensation increases as a volume of the orthodontic bracket increases, and a distance between the tooth surface (surface of the tooth) and the wire increases to reduce adjustability in tooth position.
Orthodontic force applied to the tooth is applied to the orthodontic bracket instead of a center of gravity or a center of resistance. The above-described orthodontic force that does not pass through the center of resistance of the tooth unavoidably generates rotational moment. As a result of this rotational moment, the teeth ligated by the arch wire rotate with respect to a portion around the bracket slot. When explained in more detail with reference to FIG. 1, when the rotational moment is unintentionally generated by accompanying movement of another tooth or rotational moment M is applied to an orthodontic bracket 201 by applying torque bend or third order bend to an arch wire 203 because a degree of buccolingual inclination of a tooth T has a problem, the tooth T rotates with respect to the arch wire 203 inserted into the bracket slot, and as a result, the degree of buccolingual inclination of the tooth and also a vertical height of an end (incisal edge or cusp tip) of the tooth may be changed. As the bracket slot is spaced further away from the tooth surface (i.e., as the bracket profile is raised), the above-described problem becomes further serious.
In particular, in case of the lingual orthodontic treatment, when a stock bracket is used instead of a customized bracket, the arch wire 203 that is the rotational center of the tooth T is spaced further away from the tooth surface to significantly increase height difference between incisal edges of the tooth T after/before the orthodontic treatment as in FIG. 1.
Accordingly, as the distance from the tooth surface to the arch wire 203 increases, an amount additionally height-adjusted remarkably increases when the degree of buccolingual inclination of the tooth T is adjusted.
Also, when the distance from the tooth surface to the arch wire 203 increases, since the orthodontic force is applied further away from the central point or the center of resistance of the tooth T as the distance from the tooth surface or the incisal edge, which moves even when horizontal or vertical movement is performed, to the arch wire 203 increases, movement accompanied by the rotational moment instead of only horizontal or vertical movement occurs, and this rotational moment is difficult to be appropriately adjusted, thereby hardly performing the ideal orthodontic treatment.
Accordingly, it is desired that the distance between the bracket slot, into which the arch wire 203 is mounted, and the tooth surface is minimized when the orthodontic bracket 201 is fabricated.
On the other hand, as another related art, a technique regarding ‘MODULAR SYSTEM FOR CUSTOMIZED ORTHODONTIC APPLIANCES’ is disclosed in Korean Patent Publication No. 10-0647356 as in FIG. 2.
This patent technique imports an orthodontic bracket 301 in which a linear bracket slot is pre-formed from an established library of a virtual bracket body pre-stored as a digital shape data in a computer to align the orthodontic bracket 301, and then an arch wire 303 corresponding to the alignment of the orthodontic bracket is designed.
Here, since the orthodontic bracket is firstly aligned and then the arch wire is designed, as a result, the arch wire is spaced away from the tooth surface to increase a height of the bracket profile and the irritating sensation. As above-described with reference to FIG. 1, the distance between the tooth surface and the arch wire increase to reduce the adjustability of the tooth position by the orthodontic appliance.
Also, in this related art, since the bracket body having the linear bracket slot is imported from the established library to align the orthodontic bracket, the bracket slots are separately aligned instead of aligned along the arch wire that is continuously implemented, and then a wire for orthodontic treatment (arch wire) is formed such that a distance between the neighboring linear bracket slots are connected by a separate linear line.
That is, as described in FIGS. 3A and 3B, the arch wire 303 having a shape in which the orthodontic bracket 301 is aligned and then the linear line of the bracket slot and the linear line corresponding to a region between the orthodontic brackets 301 are connected to each other and the orthodontic bracket 301 having a shape in which the arch wire 303 is bent to have a linear section corresponding to a region between a linear section corresponding to the slot and the orthodontic bracket 301 are fabricated together to be provided.
In case of the above-described method, when the mounting position of the arch wire 303 is slightly deviated from an intended position, a relationship between the arch wire and the orthodontic bracket 301 may change. Accordingly, the teeth may be aligned on positions different from the positions intended on the basis of the relationship. Also, in the malocclusion in a state in which a protruding tooth exists, the orthodontic bracket bonded to the tooth moves along the arch wire to straighten the protruding tooth, and when a bent portion between the linear lines is disposed in the slot, severe friction is generated on the portion, so that gliding movement of the wire in the slot becomes difficult and thus the teeth alignment is stopped or slowed.
That is, when the arch wire 303 is accurately mounted on the pre-intended position as illustrated in FIG. 4A, the customized arch wire 303 that is bent at every portion between the orthodontic brackets 301 may be accurately mounted. However, when the arch wire 303 is mounted to be slightly deviated (e.g. 1 mm) to the right side (or left side) from the intended position as in FIG. 4B, as a portion ‘a’ indicated by a circle and an arrow in FIGS. 4A and 4B moves, the arch wire 303 is not matched to the bracket slot. Here, when the arch wire 303 is inserted into the bracket slot, the tooth moves to an undesired position, so that the orthodontic treatment is inaccurately performed or the bent portion is disposed in the bracket slot, thereby generating severe friction to stop or slow the tooth movement
Also, since each of the bracket slots is linearly formed, like the above-described related art, in case of the labial orthodontic treatment, the arch wire 303 substantially contacts both end areas of the bracket slot in the longitudinal direction, and in case of the lingual orthodontic treatment, the arch wire 303 substantially contacts one point of the bracket slot.
Thus, as the arc wire 303 may not completely close-contact the bracket slot, the exact pulling force and pulling position may not be expected to hardly perform the ideal orthodontic treatment.